1. Field of the Invention
This invention relates to a process for improving resistance of pressure vessel shells, tubesheets, tubes, pipes, pipe fittings and machine parts to stress corrosion cracking which comprises heating at least those portions of the pressure vessel shell, tubesheet, tube, pipe, pipe fitting and machine part subject to danger by stress corrosion cracking to a critical elevated temperature level, cooling at least the surfaces of those portions of said pressure vessel shell, tubesheet, tube, pipe, pipe fitting and machine part subject to stress corrosion cracking and then permitting said cooled surface portions to come to ambient temperature.
2. Description of the Prior Art
In our U.S. Pat. No. 4,702,880, issued Oct. 27, 1987, we discovered, and claimed, a process for improving resistance of control rod guide tube split pins in nuclear reactors to stress corrosion cracking which comprised heating said split pin to a critical elevated temperature level, cooling at least the surface portions of said split pin subject to stress corrosion cracking and then permitting said split pin to come to ambient temperature.
We have now further found that the process claimed in our U.S. Pat. No. 4,702,880 can also be used to improve resistance of pressure vessel shells, tubesheets, tubes, pipes, pipe fittings and machine parts to stress corrosion cracking when the same are placed or are used in surroundings tending to induce stress corrosion cracking therein or in a portion thereof. When pressure vessel shells, tubesheets, tubes, pipes, pipe fittings and machine parts are produced and/or are assembled high tensile residual stresses occur over their entire surfaces or over a portion thereof. Often in use these elements are in a hostile environment, for example, in situations wherein they are in contact with water under high pressure, often with the water containing dissolved oxygen and/or chemicals. Under these circumstances these elements are subject to stress corrosion cracking, particularly when they are made, in whole or in part, of stainless steel or high nickel alloys. When this happens, failure occurs, often with catastrophic results and with great loss in money.